If the database is already approximately 500GB, you only need to alter it by the difference between what is needed and the current size. (i.e. if the database is currently 500000M in size, you need only enlarge it by another 7712M).

If the device doesn't have that much free space, you would need to first either a) resize the device by at least the amount of extra space needed orb) alter onto a different device that has enough free space orc) disk init a new device and alter onto the new device